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Saturday, July 26, 2014

Look to the Roof for Energy Savings

Some design elements are problematic in and of themselves,
and some components can be problematic unless they’re installed perfectly.
Aesthetics are one thing, but practicality is another. For practical reasons,
it is imperative to get roofing details right.

CAD systems make designing a complex roof fairly easy, but
even if a roof performs fine in the modeling software, it still has to be
built, insulated, and air-sealed to specs. A simple gable or hip roof, or as
close a design as you can come up with, will reap rewards for the designer,
builder, homeowner, and remodeler.

“Chopped-up roofs with a variety of intersecting planes are
hard to frame, hard to keep watertight, and hard to vent,” said former builder
Martin Halladay, who writes for Green Building Advisor. “Every nook and
cranny creates somewhere for pine needles and ice to accumulate. You don’t want
any nooks and crannies on your roof.”

Roof design doesn’t have to be complex to look good, and
simple designs are more functional, cheaper, and easier to re-roof. Plus,
simple roof designs offer more space for installation of PV panels.

Another key to ensuring good practice is to ditch the idea
of skylights, or “roof windows,” as they’re sometimes called. Since they are
really windows, they’ll perform as such, with an R-value of about two to four.
This means you can have a well-insulated, high-performance roof that’s built to
last, combined with a few holes that waste a lot of energy.

“A skylight in the roof of a house will typically lose 35
percent to 45 percent more heat during cold weather than the exact same window
installed on the side of the house,” say the writers atEnergy Realist. “That’s
because heated air rises.”

Skylights can let massive amounts of heat into a home, as
well.Energy Realist states that “a 2-foot by 4-foot skylight made with a
single pane of clear glass will allow enough heat into a home to make a typical
air conditioner use an additional 240 kilowatt hours of electricity per year.
Based on an average kWh rate of about 8 cents, that means that one clear
skylight could boost your electric bills about $19 per year for extra cooling.”

They are also prone to leaking. Although manufacturers have
certainly made great strides in preventing skylight leaks, a lot depends on the
quality of installation, so the potential for leaks will always be present.

“In one place we could poke a pencil through gaps in the
flashing, on all four corners, to the outside air,” said one Energy
Realistwriters, who works as a home energy auditor, of a particular
installation.

Another roof hole that’s easy to avoid is downlights or
recessed can lights in insulated ceilings. They’re notoriously hard to seal,
and therefore allow air to flow back and forth into and out of the conditioned
space. They also permit moisture to flow, which can lead to moisture issues in
attic insulation. And finally, a lot of heat can move into the cooler space,
whether that’s the attic or interior space, through leaky fixtures.

This test of light bulbs demonstrates how much heat even LED
bulbs generate:

An LED
lamp at 28°C room temperature showed a heat sink temperature of 60°C to
100°C depending on the make and model of the LED bulb, room temperature
and airflow.

A CFL
lamp in the same test was running a glass temperature of 120°C and
electronics temperature of 85°C.

Incandescent
and halogen bulbs were as hot as 181°C, and sections of the glass on a CFL
bulb were as hot as 131°C

While there are plenty of ways to ensure good design, a look
at oft-ignored roof issues shows how simple common sense can save money, hassle
and headaches down the line.